The present invention relates to a control method for an electric power steering apparatus for a vehicle.
As a conventional motor controller for an electric power steering apparatus for a vehicle, an apparatus which has a torque sensor for detecting a torque based on a steering operation of a steering wheel performed by a driver (or operator), and controls a rotational direction and a rotational torque of a motor in accordance with an output signal from the torque sensor is known (Japanese Patent Publication No. 45-41246).
In an electric power steering apparatus for a vehicle, a power steering unit consisting of a motor and reduction gears suffers from a large inertia unlike in a conventional hydraulic steering apparatus. When the inertia is large, a mechanism cannot be easily moved and once the mechanism moves, it cannot be easily stopped. For this reason, if a self-aligning torque (force for returning a steering wheel) is increased in a high-speed state, the steering wheel is not stopped at the center and is turned toward the opposite side by its returning force, thus impairing convergence. Since the movement of the steering wheel is not sharp due to the inertia even in a low-speed state, the power steering apparatus performs return control for returning the steering wheel, thus further impairing convergence.